1. The Field of the Invention
This invention concerns improvements in and relating to monitoring, particularly, but not exclusively for alpha emitter contamination on surfaces and/or long items.
2. The Relevant Technology
Instruments for detecting alpha emission are known but they are restricted in their applicability. Techniques in which the detector must be brought into very close proximity with the entire surface of the item to be monitored, i.e., closer than 5 cm, are problematical in implementing and time consuming to operate.
Other detectors, based around the detection of ions generated by alpha particle emission, are restricted to applications in which the item to be monitored is small enough to be completely enclosed for the purposes of monitoring.
The present invention aims to provide a system for monitoring surfaces and/or large and particularly long items effectively whilst obtaining a true and accurate reading.
According to a first aspect of the invention we provide an instrument for monitoring alpha emitting sources on an item or location, the instrument comprising a detecting chamber defining a detecting volume, the detecting chamber being provided with an opening/inlet to which portions of the item or location can be presented, and with one or more electrodes for discharging ions produced in the detecting volume, the instrument further being provided to monitor ions discharged on the electrode(s), the opening/inlet to the detecting chamber being open to the presentation or passage of different portions of the item or location whilst sealing means are provided to reduce, and preferably at least substantially eliminate, the passage of ions from outside the detecting volume to within the detecting chamber.
In this way the presentation of an item or location to the instrument is possible, whilst avoiding false readings from ambient ions.
The detection chamber may be provided with an opening in one side. The opening may form a part or the whole of that side. The detection chamber may be in the form of a hood. The item/location may pass across the front of the opening. A gap between the edges of the chamber and the item/location may be provided.
The detecting chamber may be provided with an inlet and an outlet, the inlet to the detecting chamber being open to the passage of an item/location to be monitored from outside the chamber to inside the chamber, the inlet being closed to the passage of ions from outside the chamber to inside the chamber, the outlet from the detecting chamber being open to the passage of an item/location to be monitored from inside the chamber to outside the chamber, the outlet being closed to the passage of ions from outside the chamber to inside the chamber.
An instrument with an enclosing detecting chamber may thus be provided.
The chamber is preferably provided with an inlet and outlet on a common axis. The chamber may be cylindrical. The inlet and/or outlet may be provided in the end wall(s) of the cylinder.
The inlet and/or outlet may be provided within a further chamber. Preferably the inlet and outlet are each provided in a further chamber. The further chamber(s) may be provided with an opening to the surrounding environment. Preferably the further chamber aperture is axially aligned with the aperture (inlet/outlet) into the chamber. Most preferably the aperture of the inlet further chamber, the inlet to the chamber, the outlet from the chamber, and the aperture in the outlet further chamber are all axially aligned.
The inlet and/or outlet further chamber may be cylindrical.
The opening and/or inlet and/or outlet may be closed to the passage of ions into the chamber by an electric field. The sealing means may comprise means for generating an electric field.
The opening and/or inlet and/or outlet may be provided with one or more electrodes.
Where an opening is provided preferably the sealing means are provided in proximity to the gap. The sealing means may be provided around the external periphery of the gap. Continuous or a number of discrete sealing means may be provided.
Preferably the sealing means comprises one or more electrodes, most preferably planar electrode(s). The electrode(s) may be parallel to the item/location and/or to the detecting electrode.
Where an inlet and/or an outlet are provided preferably the electrode(s) are provided in further chamber(s).
An electrode extending along the axis of the inlet and/or outlet may be provided. The electrode may surround or substantially surround the axis of the inlet and/or outlet. A cylindrical electrode may be provided.
A plurality of electrodes may be provided extending along the axis of the inlet and/or outlet. The electrodes are preferably provided in opposition to at least one, and preferably all sides of the item/location. The electrodes may be provided in opposition to one another on opposing sides of the axis of the inlet and/or outlet. Two or more planar electrodes may be provided. A potential difference between the opposing electrodes may be used. Preferably the electrodes are at a different potential to the item/location. Most preferably the electrodes are at the same potential.
A potential difference between the electrode(s) and the item/location is preferably employed. Preferably the item/location is grounded or at least at a reduced potential compared with the electrode(s). Preferably an electric field of at least 50 Vcmxe2x88x921 separation between the electrode(s) and item/location is provided. A level of at least 75 Vcmxe2x88x921 and more preferably of at least 100 Vcmxe2x88x921 may be provided.
The potential may be an AC potential, but a DC potential is preferred.
The electrode(s) may be provided in proximity to the position occupied by the item/location in use. A separation of less than 20 cm may be provided, but preferably the separation is less than 10 cm or even less than 3 cm.
The opening and/or inlet and/or outlet to the chamber may be sealed to the passage of ions by a magnetic field.
Where an opening is provided preferably the magnetic field is generated around the gap and/or the periphery of the opening.
Where an inlet and/or outlet is provided preferably the magnetic field is generated within further chamber(s).
Preferably the magnetic field is configured to repel ions approaching entrance to the detecting volume and/or the inlet and/or outlet. Electromagnets and/or permanent magnets may be provided.
The detection chamber may be provided with one or more, preferably pairs of, opposing detection electrodes. Preferably the electrodes of a pair are provided such that the item passes between them. A potential difference between the opposing electrodes of a pair is preferably generated in use. An applied or electrostatic potential may be employed.
The detection chamber may be provided with one or more electrodes opposing the item/location. An applied potential or electrostatic potential may be employed.
The means for monitoring ions discharged on the electrode(s) may comprise electrostatic charge monitoring means. More preferably the means for monitoring ions discharged on the electrode(s) comprise current indicating means and more preferably current measuring means, such as an electrometer.
Preferably one or more of the electrodes is connected to an electrometer.
The item/location may be a surface, such as an area of floor, wall, ceiling, soil, rubble, part of the surface of a piece of equipment, such as a glove box, material traveling on a conveyor, or a discrete item such as a pipe, beam (such as an I beam), pole, fuel cladding, fuel element, cable, wire, rail or other elongate or large item.
The instrument may be provided with associate means for supporting the item/location and/or moving the item/location through the instrument. Such means may be provided on both sides of the instrument.
The instrument may be provided with means for supporting it on the item/location to be monitored. The support means may enable the instrument to be moved along the item and/or over the location.
According to a second aspect of the invention we provide a method of monitoring alpha emitting sources on an item or location, the method comprising presenting a portion of the item or location to an opening or inlet connected to a detecting chamber in an instrument, the detecting chamber defining a detecting volume and being provided with one or more electrodes for discharging ions produced in the detecting volume, the method including monitoring ions discharged on the electrode(s), and the method further including sealing the detecting volume against the passage of ions from outside the detecting volume to within the detecting volume, whilst allowing the presentation of different portions of the item or location to the detecting chamber.
The item may be introduced by moving the item into the detector and/or by moving the detector along the item.
The second aspect of the invention includes the features, options and possibilities set out elsewhere in this application, including the steps necessary to implement them.
According to a third aspect of the invention we provide an instrument for monitoring alpha emitting sources on an item, the instrument comprising a detecting chamber defining a detecting volume, the detecting chamber being provided with an inlet through which the item can be introduced and an outlet through which the item leaves the detecting chamber, the detecting chamber being provided with one or more electrodes for collecting ions produced in the detecting volume by the portion of the item in the detecting volume, the instrument further being provided with means to monitor ions discharged on the electrode(s).
In this way the monitoring of items considerably longer than the detecting volume, and indeed the instrument, is possible.
The detection chamber may be provided with one or more electrodes opposing the portion of the item within the detection volume. A single electrode surrounding the portion of the item is preferred.
The electrode(s) are preferably configured to the cross-sectional profile of the item being monitored. A cylindrical electrode may be provided, most preferably with its axis aligned with the axis of the item and/or instrument.
An applied, preferably externally generated, potential may be employed or an electrostatic potential may be employed.
Preferably the voltage gradient between different portions of the electrode(s) and the portion of the item is substantially constant for different portions of the a electrode and of the item.
The detection chamber may be provided with one or more pairs of opposing detection electrodes. Preferably the electrodes of a pair are provided such that the item passes between them. A potential difference between the opposing electrodes of a pair may be provided in use. Preferably a potential difference between the item and at least one of the electrodes is provided in use. An applied or electrostatic potential may be employed.
The chamber is preferably provided with an inlet and outlet on a common axis. The chamber may be cylindrical. The inlet and/or outlet may be provided in the end wall(s) of a right cylinder.
The inlet and/or outlet may lead to a further chamber externally provided to the detecting chamber. The further chamber(s) may be provided with an opening to the surrounding environment. Preferably the further chamber aperture is axially aligned with the aperture (inlet/outlet) into the detecting chamber. Most preferably the aperture of the inlet further chamber, the inlet to the chamber, the outlet from the chamber and the aperture in the outlet further chamber are all axially aligned.
The detecting chamber may have an inlet closed to the passage of ions from outside the chamber to inside the chamber and/or an outlet closed to the passage of ions from outside the chamber to inside the chamber.
The inlet and/or outlet further chambers may have an internal configuration approximately conforming to the external configuration of the item. A limited clearance, most preferably over a significant length may be provided between the internal surface of the further chamber(s) and the external surface of the item. The clearance may be less than 5 mm and more preferably less than 2 mm. The significant length may be greater than 10 cm and more preferably greater than 25 cm. The length may be at least 5 times, more preferably at least 10 times and ideally at least 20 times the minimum clearance presented.
The detection chamber may be provided with alternative means for excluding ambient ions. The atmospheric pressure in the detection chamber may be higher than the ambient atmospheric pressure.
The means for monitoring ions discharged on the electrode(s) may comprise electrostatic charge monitoring means. Preferably the means for monitoring ions discharged on the electrode(s) comprise current indicating means and more preferably current measuring means. A ground referenced electrode may be provided.
Preferably one or more of the electrodes is connected to an electrometer.
The item may be a continuous item of more than 5 cm, preferably of more than 10 m, more preferably more than 20 m and potentially 50 m or more in length.
The item may be a discrete item such as a pipe, beam (such as an I beam), pole, fuel element, cladding, cable, wire, rail or other elongate or large item or a surface, such as a material traveling on a conveyor.
The instrument may be provided with associate means for supporting the item and/or moving the item through the instrument. Such means may be provided on both sides of the instrument.
The instrument may be provided with means for supporting it on the item to be monitored. The support means may enable the instrument to be moved along and/or over the item.
According to a fourth aspect of the invention we provide a method of monitoring alpha emitting sources on an item, the method comprising introducing the item through an inlet connected to a detecting chamber in an instrument and removing the item through an outlet in the instrument, the detecting chamber defining a detecting volume and being provided with one or more electrodes for discharging ions produced in the detecting volume by the portion of the item in the detecting volume, the method including monitoring ions discharged on the electrode(s).
The item may be introduced by moving the item into the detector and/or by moving the detector along the item.
The fourth aspect of the invention includes the features, options and possibilities set out elsewhere in this application, including the steps necessary to implement them.